The present invention relates to high pressure fuel supply pumps for gasoline engines.
Single piston, cam driven fuel pumps have become a common solution for generating high pressure fuel for common rail direct injection gasoline engines.
It is known in the industry that the pump must incorporate an outlet check valve to prevent pressure bleed back from the rail while the pump is in the intake stroke cycle. It has become an industry requirement to incorporate a pressure relief valve within the pump to protect the entire high pressure system from an unexpected excess pressure caused by a system malfunction. In order to protect the rail and fuel injectors, the pressure relief valve must be in hydraulic communication with the rail. Two executions of such hydraulic communication, in parallel with the pump flow, are described in U.S. Pat. No. 7,401,593 and U.S. Pat. No. 8,132,558. The executions described in the prior art are successful in their ability to achieve a reasonable relief pressure by hydraulically disabling the relief device during the pumping event when normal high pressure line pulsations occur.
While these executions are sufficient for current gasoline direct injection systems that operate up to about 200 Bar rail pressure, there is a significant limitation for future systems that will operate at higher pressures required to meet forthcoming emissions regulations. Because the pressure relief valve flow returns to the pumping chamber, its associated spring and spring cavity are in direct communication with the pumping chamber. This spring cavity adds significant dead volume to the pumping chamber circuit volume that must be compressed during each pumping event. Higher operating pressures require increased pressure relief valve opening pressures, higher spring loads, and increased spring cavity volume to accommodate the increased spring size. This added dead volume combined with the increased pumping pressures has a significant detrimental effect on pump efficiency.